DE69124708T2 - Internal combustion engine with a single overhead camshaft - Google Patents

Description

This invention relates to a single overhead camshaft (SOHC) internal combustion engine comprising an intake valve drive means arranged between a single camshaft rotatably disposed above a combustion chamber and a pair of intake valves for converting the rotational motion of the camshaft into the opening and closing motions of the intake valves, an exhaust valve drive means arranged between the camshaft and a pair of exhaust valves for converting the rotational motion of the camshaft into the opening and closing motions of the exhaust valves, and a cylindrical plug receiving portion arranged in a cylinder head for receiving a spark plug to be arranged at a central portion of an upper surface of the combustion chamber.

Such a SOHC internal combustion engine is conventionally known, for example, from Japanese Patent Laid-Open No. 57806/88 and the like.

In the above prior art, a plurality of intake valve side rocker arms are arranged between a pair of intake valves and a camshaft, and a pair of exhaust valve side rocker arms are arranged between a pair of exhaust valves and the camshaft, so that the pair of intake valves and the pair of exhaust valves are opened and closed by pivotally driving the individual rocker arms of cams provided on the camshaft. In addition, a connection switching mechanism is provided in the intake valve side rocker arms and capable of switching between the connection and disconnection of the rocker arms to improve the output of the engine by changing the opening and closing mode of the intake valves in accordance with the operating condition of the engine.

The intake valve side rocker arms are adjacent to each other at a location where the connection switching mechanism is provided, however, the cams for the intake valve side rocker arms and the cams for the exhaust valve side rocker arms are provided alternately in the axial direction on the camshaft, as also seen in, for example, EP-A-0 187 287, and thus the intake valve side rocker arms cannot be arranged in a compact manner. This causes an increase in size of the linkage switching mechanism, resulting in an increase in weight of the intake valve side rocker arm, difficulty in improving the dimensional accuracy of the linkage switching mechanism, and difficulty in arranging the sliding contact portion of the intake valve side rocker arm with the cam and the operatively connected position of the intake valve side rocker arm to the intake valve together in a plane perpendicular to the pivot axis of the intake valve side rocker arm, thereby causing an uneven or eccentric load acting on the intake valve side rocker arm.

Furthermore, JP-A-1 301 909 shows a SOHC internal combustion engine in which a plurality of intake valve side rocker arms are arranged between intake valves and a camshaft and a pair of exhaust valve side rocker arms are arranged between a pair of exhaust valves and the camshaft. The camshaft is supported at locations between the rocker arms.

Viewed from one aspect, the present invention provides a multi-cylinder internal combustion engine with a single overhead camshaft, comprising: a plurality of cylinders, a single camshaft rotatably mounted in a cylinder head above combustion chambers for the cylinders, the single camshaft having cams provided on it; a pair of intake valves for each cylinder mounted in the cylinder head on one side of the camshaft; a plurality of intake valve side drive rocker arms for operatively connecting the camshaft to the pair of intake valves; a pair of exhaust valves for each cylinder mounted on the cylinder head on the other side of the camshaft; a pair of exhaust valve side drive rocker arms for operatively connecting the camshaft to the pair of exhaust valves; an arrangement for rotatably supporting the camshaft to the cylinder head; a spark plug mounting hole in a central portion of a ceiling of each combustion chamber; and a plug tube extending to the spark plug mounting hole and provided in an inclined manner with its upper portion spaced from the camshaft, the spark plug tube being disposed substantially between the camshaft and the axes of the pair of exhaust valves; wherein the plurality of intake valve side drive rocker arms are disposed between the pair of exhaust valve side drive rocker arms, characterized in that the bracket assembly comprises adjacent two brackets coupled to the cylinder head, the adjacent two brackets each being disposed between two adjacent cylinders and forming adjacent brackets for the camshaft, and wherein the plurality of intake valve side drive rocker arms and the pair of exhaust valve side drive rocker arms are all disposed between the adjacent two brackets at a location substantially above the associated cylinder are arranged; wherein the cams for operating the intake and exhaust valve side drive rocker arms for each cylinder are all arranged between the adjacent two brackets, the cams for the exhaust valve side drive rocker arms being arranged at the opposite outermost positions; and wherein a mechanism is provided for switching between the connection and the disconnection between adjacent ones of the intake valve side drive rocker arms.

With such a construction, the opening and closing mode of the intake valves in the intake valve driving mechanism can be changed in accordance with the operating state of the engine by switching between the connection and the disconnection of the plurality of rocker arms by operating the connection switching mechanism in accordance with the operating state of the engine. This can contribute to improving the output from the engine. Furthermore, the intake valve driving means and the camshaft can be made compact by arranging the plurality of rocker arms constituting the intake valve driving means adjacent to each other. Consequently, the connection switching mechanism provided in the intake valve driving means can also be made compact.

Several embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figures 1 to 4 show a first embodiment of the present invention, wherein

Figure 1 is a longitudinal sectional view of a machine body portion taken along a line I-I in Figure 2 ;

Figure 2 is a sectional view taken along a line II-II in Figure 1;

Figure 3 is a sectional view taken along a line III-III in Figure 1; and

Figure 4 is an enlarged sectional view taken along a line IV-IV in Figure 1;

Figures 5 and 6 illustrate a second embodiment of the present invention, wherein

Figure 5 is a longitudinal sectional view of a machine body portion similar to that in Figure 1; and

Figure 6 is a sectional view taken along a line VI-VI in Figure 5; and

Figures 7 to 9A illustrate a third embodiment of the present invention, wherein

Figure 7 is a longitudinal sectional view of a machine body portion similar to that of Figure 1;

Figure 8 is a sectional view taken along a line VIII-VIII in Figure 7;

Figure 9 is a bottom view of a cylinder head taken along a line IX-IX in Figure 7; and

Figure 9A is a diagram illustrating the shape of a pinch edge;

Figure 10 is a bottom view of a cylinder head similar to that of Figure 9, but showing a modification of an intake passage;

Figures 11 and 12 illustrate a fourth embodiment of the present invention, wherein

Figure 11 is a longitudinal sectional view of a machine body portion similar to that of Figure 1; and

Figure 12 is a sectional view along a line XII-XII in Figure 10.

Turning first to Figure 1, which illustrates a first embodiment of the present invention, an essential part of an engine body in a SOHC multi-cylinder internal combustion engine includes a cylinder block 1 and a cylinder head 2 coupled to an upper surface of the cylinder block 1. A piston 4 having a recess 4a on its upper surface is slidably received in a cylinder 3 provided in the cylinder block 1, and a combustion chamber 5 is defined between the upper surface of the piston 4 and the cylinder head 2.

Turning also to Figure 2, first and second intake valve ports 61 and 62 and first and second exhaust valve ports 71 and 72 are provided in the cylinder head 2 and open to an upper surface of the combustion chamber 5. The intake valve ports 61 and 62 are connected to a single intake port 8 opened in one side surface of the cylinder head 2 and the exhaust valve ports 71 and 72 are connected to a single exhaust port 9 opened in the other side surface of the cylinder head 2. A first VI1 and a second intake valve VI2 are provided in a pair of cylindrical guides 10 respectively disposed in the cylinder head 2 and adapted to open and close the first and second intake ports 6₁ and 6₂ independently. Coil valve springs 12, 12 surrounding the intake valves VI1 and VI2 are provided between the cylinder head 2 and holders 11, 11 fixed to upper ends of the intake valves VI1 and VI2 respectively projecting from the corresponding cylindrical guides 10 so that the intake valves 12, 12 are biased upward, that is, in the valve closing direction, by the valve springs 12, 12. Exhaust valves VE1 and VE2 capable of opening and closing the first and second exhaust valve ports 7₁ and 7₂ are provided. to open and close independently are slidably received in a pair of cylindrical guides arranged in the cylinder head 2. Coil valve springs 15, 15 surrounding the exhaust valves VE1 and VE2 are provided between the cylinder head 2 and holders 14, 14 fixed to the upper ends of the exhaust valves VE1 and VE2 which respectively project from the cylindrical guides 13, so that the exhaust valves VE1 and VE2 are biased upward, ie in the valve closing direction, by the valve springs 15, 15.

An intake valve drive means 17₁ is arranged between the intake valves VI1 and VI2 and a single camshaft 16 operatively connected to a crankshaft (not shown) at a reduction ratio of 1/2, for converting the rotary motion of the camshaft 16 into the opening and closing movements of the intake valves VI1 and VI2, and an exhaust valve drive means 18₁ is arranged between the exhaust valves VE1 and VE2 and the camshaft 16 for converting the rotary motion of the camshaft 16 into the opening and closing movements of the intake valves VE1 and VE2.

Turning further to Figure 2, the camshaft 16 is connected to the cylinder head 2 and a camshaft 18 coupled holder 20 and has a horizontal axis perpendicular to the axis of the cylinder 3. The camshaft 16 is formed integrally with a high-speed cam 21 and low-speed cams 22, 22 adjacent to opposite sides of the high-speed cam 21 and further formed integrally with exhaust valve cams 23, 23 on opposite sides of the low-speed cams 22, 22. The high-speed cam 21 has a shape that allows the intake valves VI1 and VI2 to be opened and closed in a high-speed operating range of the engine and includes a base circular portion 21a and a raised portion 21b extending radially outward from the base circular portion 21a. Each of the low speed cams 22 has a shape that allows the intake valves VI1 and VI2 to be opened and closed in a low speed operating range of the engine, and includes a base circular portion 22a and a raised portion 22b extending radially outward from the camshaft 16 with a smaller height than that of the raised portion 21b of the high speed cam 21 and over a smaller central angular range than that of the raised portion 21b. Further, the exhaust valve cam 23 has a shape that allows the exhaust valves VE1 and VE2 to be opened and closed in all operating conditions of the engine.

The intake valve drive means 17 comprises a first drive rocker arm 24₁ operatively connected to the first intake valve VI1, a second rocker arm 25₁ connected to the second intake valve VI2, and a free rocker arm 26₁ disposed between the drive rocker arms 24₁ and 25₁. The rocker arms 24₁, 25₁ and 26₁ are pivotally supported by a rocker arm shaft 27 which is fixedly held on a bracket 20 and has an axis parallel to the camshaft 16 above the camshaft 16. The Exhaust valve drive means 18₁ includes a pair of exhaust valve side rocker arms 29₁ and 30₁ pivotally supported on a rocker arm shaft 28 fixed to the bracket 20 parallel to the rocker arm shaft 27 above the camshaft 16.

In the intake valve driving means 17₁, a cam slider 31 is provided at one end of the first drive rocker arm 24₁ and adapted to come into sliding contact with the low-speed cam 22 provided on the camshaft 16, and a cam slider (not shown) is provided at one end of the second drive rocker arm 25₁ to come into sliding contact with the low-speed cam 22 provided on the camshaft 16. A cam slider (not shown) is provided on the free rocker arm 26₁ to come into sliding contact with the high-speed cam 21 provided on the camshaft 16. In addition, a cam slider 34 is provided at one end of each of the exhaust valve side rocker arms 29₁ and 30₁. provided to come into sliding contact with the corresponding one of the exhaust valve cams 23, 23 provided on the camshaft 16.

An adjusting screw 35 is threadedly engaged with the other end of each of the first and second drive rocker arms 24₁ and 25₁ of the intake valve drive means 17₁ for combined forward and backward movement to abut against an upper end of each of the intake valves VI1 and VI2 such that the intake valves VI1 and VI2 are opened and closed in response to the pivotal movement of the drive rocker arms 24₁ and 25₁. An adjusting screw 36 is further connected to the other end of each of the rocker arms 29₁ and 30₁ in the exhaust valve drive means 18₁. in threaded engagement to abut against an upper end of each of the exhaust valves VE1 and VE2 such that the exhaust valves VE1 and VE2 are opened and closed in response to the pivotal movement of the rocker arms 29₁ and 30₁.

Referring again to Figure 1, a support plate 37 is fixedly mounted on the bracket 20 above the cylinder head 2 in a position corresponding to a position between adjacent cylinders 3 to cover the rocker arm shafts 27 and 28. The support plate 37 is provided with a lost motion mechanism 38 to bias the free rocker arm 26₁ against the high speed cam 21.

The lost motion mechanism 38 includes a bottomed cylindrical guide member 39 incorporated in the support plate 37, a piston 40 slidably received in the guide member 39 and having an abutment portion convergently shaped at an end closer to the free rocker arm 26₁ for abutment against the free rocker arm 26₁, a stopper 41 releasably secured to an inner surface of the guide member 39 closer to an open end for engaging the piston 40, and a first spring 42 and a second spring 43 disposed between the piston 40 and the guide member 39 for resiliently biasing the piston 40 toward abutment against the free rocker arm 26₁.

The support plate 37 is provided with a bottomed cylindrical portion 37a which is opened downward at a position corresponding to the free rocker arm 26₁, and the guide member 39 is fitted into the bottomed cylindrical portion 37a with its open end facing downward. A spring space 44 is defined between the piston 40 and the guide member 39. The first spring 42 has a relatively small spring constant and is provided in a compressed manner between a holder 45 contained in the spring space 44 and the piston 40, and the second spring 43 has a relatively large spring constant and is provided in a compressed manner between the holder 45 and a closed end of the guide element 39 is provided.

The bottomed small hole 40b is coaxially formed in an inner surface of a closed end of the piston 40, and the first spring 42 having a relatively small spring constant is enclosed in the small hole 40b, thereby preventing the first spring from falling. The stopper portion 40a of the piston 40 further has a vent hole 46 formed therein in a cross-shaped opening in an outer surface of the stopper portion 40a and communicating with the outside of the spring chamber 44 to prevent the interior of the spring chamber 44 from being internally pressurized or depressurized during the sliding movement of the piston 40.

Further, a lubrication groove 47 is provided on the support plate 37 so as to extend parallel to the camshaft 16 adjacent a base end of the bottomed cylindrical portion 37a, and a lubrication groove 48 is provided in the base end of the bottomed cylindrical portion 37a and the guide member 39 for guiding an oil flow through the lubrication groove 47 into the spring chamber 44. Thus, lubrication oil can be supplied between the piston 40 and the guide member 39 by flowing the lubrication oil through the lubrication groove 47.

Turning to Figure 4, the intake valve drive means 17 is provided with a connection switching mechanism 50 capable of switching between the connection and the disconnection of the rocker arms 24₁ to 26₁ in accordance with the operating state of the engine.

The connection switching mechanism 50 comprises a first connecting piston 51 which connects the first drive rocker arm 24₁ and the free rocker arm 26₁, a second connecting piston 52 which can couple the free rocker arm 26₁ and the second drive rocker arm 25₁, a limiting member 53 for limiting the movement of the first and second connecting pistons 51 and 52, and a return spring 54 for biasing the pistons 51 and 52 and the limiting member 53 toward a decoupling position.

A first bottomed guide hole 55 is provided in the first drive rocker arm 24₁ parallel to the rocker arm shaft 27 and open toward the free rocker arm 26₁. The first connecting piston 51 is slidably received in the first guide hole 55, and a hydraulic pressure chamber 56 is defined between one end of the first connecting piston 51 and a closed end of the first guide hole 55. Further, a communication passage 57 is provided in the first drive rocker arm 24₁ so as to communicate with the hydraulic pressure chamber 56, and a hydraulic pressure supply passage 58 is provided in the rocker arm shaft 27 and leads to a hydraulic pressure supply source, not shown. The hydraulic pressure supply passage 58 is continuously communicated with the communication passage 57 and the hydraulic pressure chamber 56 via an internal groove (not numbered) in the first drive rocker arm 24₁, regardless of the swinging state of the first drive rocker arm 24₁.

A guide hole 59 corresponding to the first guide hole 55 is provided in the free rocker arm 26₁ so as to extend parallel to the rocker arm shaft 27 between opposite side surfaces thereof, and the second connecting piston 52, which abuts at one end against the other end of the first connecting piston 51, is slidably received in the guide hole 59.

A second bottomed guide hole 60 corresponding to the guide hole 59 is provided in the second drive rocker arm 251 parallel to the rocker arm shaft 27 and open to the free rocker arm 261. The bottomed cylindrical restricting member 53 abuts against the other end of the second connecting piston 52 and is slidably received in the second guide hole 60. The restrictor 53 is disposed with its open end facing the closed end of the second guide hole 60, and a radially outwardly extending edge 53a at such open end is in sliding contact with an inner surface of the second guide hole 60. The return spring 54 is mounted in a compressed manner between the closed end of the second guide hole 60 and a closed end of the restrictor 53 so that the pistons 51 and 52 and the restrictor 53 abut against each other and are biased toward the hydraulic pressure chamber 56 by the spring force of the return spring 54. Further, a communication hole 61 for venting air and oil is provided at the closed end of the second guide hole 60.

A retaining ring 62 is installed on an inner surface of the second guide hole 60 and is capable of engaging with the edge 53a of the restricting member 53 such that the restricting member 53 is prevented from slipping out of the second guide hole 60 by the restricting member 62. Further, the installed position of the retaining ring 62 is restricted such that the further movement of the restricting member 53 toward the free rocker arm 26₁ from a state in which it is in abutment against the free rocker arm 26₁ to a location corresponding to a plane between the free rocker arm 26₁ and the second drive rocker arm 25₁ is prevented.

In the link switching mechanism 50, a pivot pin 63 is installed in the side surface of each of the first and second drive rocker arms 24₁ and 25₁ facing the free rocker arm 26₁ to engage with the free rocker arm 26₁ while allowing the relative pivotal movement of the drive rocker arms 24₁ and 25₁ with the free rocker arm 26₁.

Referring again to Figs. 1 and 2, a spark plug 64 is disposed at a central portion of an upper surface of the combustion chamber 5. A plug tube 65 is disposed in the cylinder head 2 and serves as a cylindrical plug receiving portion for receiving the spark plug 64. The pair of exhaust valve side rocker arms 29₁ and 30₁ constituting the exhaust valve driving means 18₁ are disposed for sliding contact with the exhaust valve cams 23, 23 of the camshaft 16 on opposite sides of the intake rocker arms 24₁, 25₁ and 26₁ disposed adjacent to each other to constitute the intake valve driving means 17₁. This ensures that a relatively large space is provided between the exhaust valve rocker arms 29₁ and 30₁. and 30₁, and the exhaust valves VE1 and VE2 can be arranged at a relatively large distance from each other. Therefore, the plug tube 65 is positioned in the cylinder head 2 such that its axis is arranged between the exhaust valves VE1 and VE2, i.e., it is located between the exhaust valves VE1 and VE2 as well as between the exhaust valve side rocker arms 29₁ and 30₁. The plug tube 65 is inclined so that its upper portion is spaced from the camshaft 16. The spark plug 64 inserted into the plug tube 65 is threadedly mounted in the cylinder head 2 at the central portion of the upper surface of the combustion chamber 5.

The operation of the first embodiment will be described. When the engine is in a low speed operation , the hydraulic pressure in the hydraulic pressure chamber 56 in the link switching mechanism 50 is lowered, and the pistons 51 and 52 and the restrictor 53 are in their uncoupled states in which they have been moved to the hydraulic pressure chamber 56 to the maximum extent by the spring force of the return spring 54. In such a state, the abutting surfaces of the first and second link pistons 51 and 52 are located between the first drive rocker arm 24₁ and the free rocker arm 26₁, while the abutting surfaces of the second link piston 52 and the restrictor 53 are located between the free rocker arm 26₁ and the second drive rocker arm 25₁. Therefore, the rocker arms 24₁, 25₁ and 26₁ are in an uncoupled state so that relative angular displacement is permitted.

In such a decoupled state, the rotation of the camshaft 16 causes the first and second drive rocker arms 24₁ and 25₁ to swing in response to the sliding contact with the low-speed cams 22, 22, so that the intake valves VI1 and VI2 are opened and closed at a timing and a lift amount corresponding to the shape of the low-speed cams 22, 22. During this time, the free rocker arm 26₁ is swing in response to the sliding contact with the high-speed cam 21, but its swinging motion does not exert any influence on the first and second drive rocker arms 24₁ and 25₁. In addition, the exhaust valves VE1 and VE2 are opened and closed with a timing and a lift height that corresponds to the shape of the exhaust valve cams 23, 23.

During high speed operation of the engine, a higher hydraulic pressure is supplied to the hydraulic pressure chamber 56. This causes the first and second connecting pistons 51 and 52 as well as the limiting element 53 in the connection switching mechanism 50 of the Intake valve driving means 17₁ are moved toward the connecting pistons against the spring force of the return spring 54 so that the first connecting piston 51 is inserted into the guide hole 59 while at the same time the second connecting piston 52 is inserted into the second guide hole 60, thereby connecting the rocker arms 24₁, 25₁ and 26₁. At this time, the amount of swinging movement of the free rocker arm 26₁ in sliding contact with the high-speed cam 21 is the largest and therefore the first and second driving rocker arms 24₁ and 25₁ are swung with the free rocker arm 26₁ and the intake valves VI1 and VI2 are opened and closed at a timing and a lift amount corresponding to the shape of the high-speed cam 21.

During this high speed operation, the exhaust valve side rocker arms 29₁ and 30₁ still open and close the exhaust valves VE1 and VE2 with a timing and lift height that corresponds to the shape of the exhaust valve cams 23, 23 as during the low speed operation.

It is possible to provide an improvement in the output of the engine with a valve operation characteristic designed for the operating state of the engine by changing the opening and closing mode of the intake valves VI1 and VI2 between the high and low speed operation in this way.

In such an internal combustion engine, the rocker arms 24₁, 25₁ and 26₁ constituting the intake valve driving means 17₁ are arranged adjacent to each other at a position corresponding to the camshaft 16 and can be arranged together in a compact manner. It follows that the connection switching mechanism 50 is also arranged in a compact manner. This enables not only a simple improvement in the dimensional accuracy of the components of the However, the connection switching mechanism 50 to provide a smooth operation of the connection switching mechanism 50 also contributes to a weight reduction of the rocker arms 24₁, 25₁ and 26₁. Moreover, the sliding contact positions of the first and second drive rocker arms 24₁ and 25₁ to the low speed cams 22, 22 and the operatively connected positions of these rocker arms to the intake valves VI1 and VI2 can be established within a plane substantially perpendicular to the axis of the rocker arm shaft 27, thereby avoiding the effect of an uneven or eccentric load on the first and second rocker arms 24₁ and 25₁.

The plug tube 65 is arranged in the cylinder head 2 with its axis located between the exhaust valves VE1 and VE2, thereby effectively utilizing the space created by positioning the exhaust valve side rocker arms 291 and 301 on opposite sides of the intake valve drive means 171. Therefore, it is possible to make the entire arrangement more compact.

Figures 5 and 6 illustrate a second embodiment of the present invention, wherein parts that are similar to or identical to parts in the first embodiment described above are designated by the same reference numerals.

A camshaft 16 is rotatably supported by the cylinder head 2 and a cam holder 71 coupled to the cylinder head 2. A high-speed cam 21, low-speed cams 22, 22 on opposite sides of the high-speed cam 21, and exhaust valve side cams 23, 23 on opposite sides of the low-speed cams 22, 22 are integrally provided on the camshaft 16 in an arrangement similar to that shown in Figure 3, which is the first embodiment. A rocker shaft 70 parallel to the camshaft 16 is provided in the cylinder head 2 under the camshaft 16. An intake valve drive means 17₂ is provided between the intake valves VI1 and VI2 and the camshaft 16 for converting the rotary motion of the camshaft 16 into the opening and closing movements of the intake valves VI1 and VI2, and an exhaust valve drive means 18₂ is provided between the exhaust valves VE1 and VE2 and the camshaft 16 for converting the rotary motion of the camshaft 16 into the opening and closing movements of the exhaust valves VE1 and VE2.

The intake valve drive means 17₂ includes a first drive rocker arm 24₂ operatively connected to the first intake valve VI1, a second drive rocker arm 25₂ operatively connected to the second intake valve VI2, and a free rocker arm 26₂ disposed between the drive rocker arms 24₂ and 25₂. The rocker arms 24₂, 25₂ and 26₂ are pivotally supported at their base ends on the rocker arm shaft 70. The exhaust valve drive means 18₂ includes exhaust valve side rocker arms 29₂ and 30₂ which are pivotally supported at their base ends on the rocker arm shaft 70 and are separately operatively connected to the exhaust valves VE1 and VE2.

In the intake valve driving means 17₂, a cam slider 72 is provided at a middle upper portion of the first drive rocker arm 24₂ to come into sliding contact with the low speed cam 22 (see Fig. 3); a cam slider 73 is provided at a middle upper portion of the second drive rocker arm 25₂ to come into sliding contact with the low speed cam 22 (see Fig. 3); and a cam slider 74 is provided at the free rocker arm 26₂ to come into sliding contact with the high speed cam 21 (see Fig. 3). In addition, cam sliders 75 and 76 are provided at middle upper portions of the exhaust valve side rocker arms 29₂ and 30₂ to come into sliding contact with the exhaust valve cams 23, 23 (see Figure 3).

A lost motion mechanism 38' having the basically same structure as that of the lost motion mechanism 38 in the first embodiment is provided in the cylinder head 2 to bias the free rocker arm 26₂ in the intake valve drive means 17₂ toward the camshaft 16.

Further, a connection switching mechanism (not shown) having basically the same structure as that of the connection switching mechanism 50 in the first embodiment is provided in the intake valve driving means 17₂ for switching between the connection and the disconnection of the rocker arms 24₂, 25₂ and 26₂ in accordance with the operational state of the engine.

A lubricating oil supply passage 77 is provided in the rocker arm shaft 70 in parallel with the hydraulic pressure supply passage 58, and injectors 78 are provided at the base portions of the rocker arms 24₂, 25₂, 26₂, 29₂, and 30₂, respectively, to communicate with the lubricating oil supply passage 77 in accordance with the swing positions of the rocker arms 24₂, 25₂, 26₂, 29₂, and 30₂, to discharge lubricating oil from the lubricating oil supply passage 77 to their sliding contact portions with the camshaft 16.

It should be noted that the pair of rocker arms 29₂ and 30₂ constituting the exhaust valve driving means 18₂ are arranged on opposite sides of the intake valve driving means 17₂ beyond the camshaft 16. Therefore, as in the previous embodiment, it is possible to ensure a relatively large space between the exhaust valve side rocker arms 29₂ and 30₂ and it is also possible to position the exhaust valves VE1 and VE2 at a relatively large distance from each other so that the spark plug tube 65 can be arranged in the cylinder head 2 between the exhaust valves VE1 and VE2 as well as between the exhaust valve-side rocker arms 29₂ and 30₂.

Thus, in such a second embodiment, it is possible to ensure a space for the plug tube 65 with a compact overall arrangement despite the provision of the connection switching mechanism in the intake valve driving means 17₂.

Figures 7 to 9A illustrate a third embodiment of the present invention, wherein parts similar to or identical to those in the previous embodiments are designated by the same reference numerals.

Turning to Figures 7 and 8, a camshaft 16 is rotatably supported by a cylinder head 2 and a holder 20 connected to the cylinder head 2. An intake valve drive means 17₃ is provided between the camshaft 16 and the intake valves VI1 and VI2 for converting the rotational movement of the camshaft 16 into the opening and closing movements of the intake valves VI1 and VI2, and an exhaust valve drive means 18₃ is provided between the exhaust valves VE1 and VE2 and the camshaft 16 for converting the rotational movement of the camshaft 16 into the opening and closing movements of the exhaust valves VE1 and VE2.

The intake valve drive means 17₃ comprises a first drive rocker arm 24₃ operatively connected to the first intake valve VI1 and a second drive rocker arm 25₃ operatively connected to the second intake valve VI2 and disposed adjacent to the first drive rocker arm 24₃. The rocker arms 24₃ and 25₃ are at their intermediate portions pivotally supported by the rocker arm shaft 27. The exhaust valve drive means 18₃ includes exhaust valve rocker arms 29₃ and 30₃ which are separately operatively connected to the exhaust valves VE1 and VE2 and pivotally supported at their intermediate portions by rocker arm shaft 28.

A connection switching mechanism 50' is provided in the intake valve drive means 173 for switching between the connection and the disconnection of the rocker arms 243 and 253, and comprises a connection piston 83 movable between a position where the first and second drive rocker arms 243 and 253 are connected and a position where such connection is released in response to a hydraulic pressure from the hydraulic pressure supply passage 58, which hydraulic pressure supply passage 58 is provided in the rocker arm shaft 27, a restriction member 84 slidably received in the second drive rocker arm 253 and abutting against the connection piston 83, and a connection between the restriction member 84 and the second drive rocker arm 253. arranged return spring 85 for preloading the connecting piston 83 and the limiting element 84 to a decoupling side.

In the intake valve driving means 17₃, a roller 81 is attached to one end of the first driving rocker arm 24₃ to come into rolling contact with the cam 79 integrally provided on the camshaft 16, and a slider 82 is provided to one end of the second driving rocker arm 25₃ to come into sliding contact with a raised portion integrally formed on the camshaft 16 adjacent to the cam 79. The raised portion 80 is basically formed to have an outer surface circularly running around the axis of the camshaft 16, but also to have a shape such that the second intake valve VI2 is slightly tilted in an opening direction is operated while being in a substantially closed state when the first intake valve VI1 is opened by the first drive rocker arm 24₃ in a state where the second drive rocker arm 25₃ is not connected to the first drive rocker arm 24₃. Moreover, the width of the raised portion 80 in the direction along the axis of the camshaft 16 is relatively small and the width of the slider 82 provided on the second drive rocker arm 25₃ is also small in accordance with the raised portion 80 because a very small force is transmitted therebetween.

Rollers 86 and 87 are mounted on one end of each of the exhaust valve side rocker arms 29₃ and 30₃ in the exhaust valve drive means 18₃ so as to come into rolling contact with the exhaust valve side cams 23, 23 provided on the camshaft 16 on opposite sides of the cam 79 and the raised portion 80 provided on the camshaft 16, respectively.

Thus, the pair of exhaust valve side rocker arms 29₃ and 30₃ constituting the exhaust valve driving means 18₃ are arranged on opposite sides of the intake valve driving means 17₃ beyond the camshaft 16 and therefore it is possible to ensure a relatively large space between the exhaust valve rocker arms 29₃ and 30₃. It is also possible to arrange the exhaust valves VE1 and VE2 at a relatively large distance from each other so that the plug tube 65 can be arranged in the cylinder head 2 between the exhaust valves VE1 and VE2 as well as between the exhaust valve side rocker arms 29₃ and 30₃.

Turning further to Figure 9, an intake passage 97₁ formed in the cylinder head 2 in communication with the first Intake valve port 6₁, and an intake passage 97₂ provided in the cylinder head 2 in communication with the second intake valve port 6₂ is commonly connected to an intake port 8 provided in a side surface of the cylinder head 2 for each cylinder 3. One of the intake passages, such as passage 97₁, is formed in an inwardly expanded and curved manner to extend along the inner surface of the combustion chamber 5 just in front of the first intake valve port 6₁ to provide a suction vortex of the gas from the first intake valve port 6₁ into the combustion chamber 5 when the second intake valve VI2 has become substantially inoperative.

A recess 2a is provided on a lower surface of the cylinder head 2 to form an upper surface of the combustion chamber 5, and a squish edge 98 is provided between an open edge of the recess 2a and an upper surface of the piston 4 at the top dead center. The open edge of the recess 2a is shaped such that the following edge portions are connected to each other: a first peripheral edge 2a₁ corresponding to an inner circumference of the cylinder and extending in the direction 99 of the suction vortex from the first intake valve opening 6₁ into the combustion chamber 5 from the first intake valve opening 6₁ to the first exhaust valve opening 7₁; a second peripheral edge portion 2a₂ corresponding to a peripheral edge of the circular recess 4a in the piston 4 between the first and second exhaust valve openings 7₁ and 7₂; a third peripheral edge portion 2a₃ irregularly connected between an inner circumference of the cylinder and the peripheral edge of the recess 4a between the second exhaust valve opening 7₂ and the second intake valve opening 6₂; and a fourth peripheral edge portion 2a₄ corresponding to the peripheral edge of the recess 4a between the second and first intake valve openings 6₂ and 6₁. Therefore, the Squish edge 98 has a shape as shown by the hatched area in Figure 9A and is not formed in a portion extending in the direction 99 of the suction vortex from the first intake valve port 6₁ to the first exhaust valve port 71. In the portions of the squish edge 98 corresponding to those portions between the intake valve ports 6₁ and 6₂ and between the exhaust valve ports 7₁ and 7₂, the inner periphery of the squish edge 98 is opposed to the peripheral edge of the recess 4a at the upper and central portion in the piston 4.

In such a third embodiment, in a high speed operating state of the engine, the first and second drive rocker arms 24₃ and 25₃ can be connected to each other so that the intake valves VI1 and VI2 can be opened and closed at a timing and a lift height suitable for high speed operations by the shape of the cam 79. On the other hand, in a low speed operating state of the engine, the connection of the first and second drive rocker arms 24₃ and 25₃ can be released so that the first intake valve VI1 can be opened and closed by the first drive rocker arm 24₃ in sliding contact with the cam 79 at a timing and a lift height corresponding to the shape of the cam 79 while the second drive rocker arm 25₃ in sliding contact with the raised portion 80 can be brought into a substantially inoperative state to substantially render the second intake valve VI2 inoperative. Nevertheless, the second intake valve VI2 is not entirely inoperative and can be slightly operated in the opening direction when the first intake valve VI1 is opened. This makes it possible to prevent sticking of the second intake valve VI2 in the valve seat, which would otherwise be generated if a completely closed state is maintained.

In the low speed operating state of the engine in which the second intake valve VI2 is substantially inoperative and only the first intake valve VI1 is opened and closed, a fuel-air mixture is led from the intake port 8 into the combustion chamber 5 via the intake passage 971 and the first intake valve opening 61, so that a swirl is generated in the combustion chamber 5. Further, the intake passage 971 is formed in a curved manner so as to extend tangentially along the inner surface of the combustion chamber 5 just in front of the first intake valve opening 611, so that the fuel-air mixture is drawn into the combustion chamber 5 while being swirled, causing a swirl to be effectively generated.

The fuel-air mixture introduced into the combustion chamber 5 through the first intake valve opening 61 flows in the combustion chamber 5 in the direction of the suction vortex, but since the squish edge 98 is not formed in the region from the first intake valve opening 61 to the first exhaust valve opening 71 in the direction 99 of the suction vortex, a squish flow can be prevented from acting on the flow just swirled through the first intake valve opening 61 into the combustion chamber 5 in a direction that would otherwise destroy the swirl of such a flow, effectively forming a vortex in the combustion chamber 5.

Further, the inner periphery of the squish edge 98, unlike the peripheral edge of the recess 4a, is formed at a central portion of the upper surface of the piston 4 between the intake valve openings 61 and 62 as well as between the exhaust valve openings 71 and 72, and therefore a swirling flow is easily generated along the inner surface of the combustion chamber 5, making it possible to form a more effective swirl in the combustion chamber 5.

It is possible to provide an improvement in the combustion properties by creating a strong vortex in the combustion chamber 5 in this way.

It should be noted that the first drive rocker arm 24₃, which operates in a low speed range in which the component of the friction loss in the entire engine in the valve operating system accounts for a larger proportion, is in rolling contact with the cam 79 via the roller 81, and this can contribute to a reduction in friction loss due to the valve operating system in the low speed range and, consequently, to a reduction in friction loss in the entire engine. Moreover, since the exhaust valve side rocker arms 29₃ and 30₃ constituting the exhaust valve drive means 18₃ are also in rolling contact with the exhaust valve cams 23, 23 via the rollers 86 and 87, it is possible to further reduce the friction loss in the low speed range.

Further, the second drive rocker arm 25₃ is in sliding contact with the raised portion 80 via the slider 83, and this ensures that the width of the slider 83 can be smaller than that of the roller 81. Moreover, because the intake valve drive means 17₃ includes the pair of drive rocker arms 24₃ and 25₃, such intake valve drive means 17₃ can be constructed more compactly along the axis of the camshaft 16, compared with the intake valve drive means constructed of three rocker arms as in the first and second embodiments described above.

Moreover, as in the above embodiments, the overall structure can be made compact despite the provision of the connection switching mechanism 50' in the intake valve driving means 173.

In the above third embodiment, the intake passage 971 has been formed in a curved manner just in front of the first intake valve opening 61, however, it will be understood that the intake passage 971 may be arranged to the intake opening 8 shifted to the second intake valve opening 62, as compared with Figure 9, so as to extend substantially along the inner surface of the combustion chamber 5 over the entire length of the passage from the connection with the intake opening 8 to the first intake valve opening 61.

Figures 11 and 12 illustrate a fourth embodiment of the present invention, wherein parts similar to or identical to those in the previous embodiments are designated by the same reference numerals.

An intake valve drive means 17₄ is provided between the camshaft 16 and the intake valves VI1 and VI2 for converting the rotational movement of the camshaft 16 into the opening and closing movements of the intake valves VI1 and VI2, and an exhaust valve drive means 18₄ is provided between the exhaust valves VE1 and VE2 and the camshaft 16 for converting the rotational movement of the camshaft 16 into the opening and closing movements of the exhaust valves VE1 and VE2.

The intake valve drive means 17₄ comprises a first drive rocker arm 24₄ operatively connected to the first intake valve VI1, a second drive rocker arm 25₄ operatively connected to the second intake valve VI2, and a free rocker arm 26₄ disposed between the drive rocker arms 24₄ and 25₄ and capable of becoming free from the intake valves VI1 and VI2. The rocker arms 24₄, 25₄ and 26₄ are pivotally supported by the rocker arm shaft 27 at their intermediate portions. The exhaust valve drive means 18₄ comprises exhaust valve side rocker arms 29₄ and 30₄, which are separately operatively connected to the exhaust valves VE1 and VE2 and are pivotally supported by the rocker arm shaft 28 at their intermediate sections.

A connection switching mechanism 80 is provided in the intake valve drive means 174 and is capable of switching between the connection and the separation of the rocker arms 244, 254 and 264. On the camshaft 16, there are integrally provided a high-speed cam 21 formed to be primarily effective during high-speed operation of the engine, a low-speed cam 22 as a second cam formed adjacent to the high-speed cam 21 to be primarily effective during low-speed operation of the engine, and a raised portion 80 on the opposite side of the low-speed cam 22 adjacent to the high-speed cam 21. Further, in the intake valve drive means 174, a roller 89 is provided at one end of the first drive rocker arm 244. is provided so as to come into rolling contact with the low-speed cam 22; a slider 90 is provided at one end of the free rocker arm 26₄ so as to come into sliding contact with the high-speed cam 21 and a slider 91 is provided at one end of the second drive rocker arm 25₄ so as to come into sliding contact with the raised portion 80. Further, the width of the raised portion 80 in the direction along the axis of the camshaft 16 is relatively small and the width of the slider 91 provided on the second rocker arm 25₄ is also small in correspondence with the raised portion 80.

Rollers 86 and 87 are mounted on one end of each of the exhaust valve side rocker arms 29₄ and 30₄ in the exhaust valve drive means 18₄ to be in rolling contact with the exhaust valve cams 23, 23, which are provided on the camshaft 16 on opposite sides of the low-speed cam 22 and the raised portion 80, respectively.

Thus, the pair of exhaust valve side rocker arms 29₄ and 30₄ constituting the exhaust valve driving means 18₄ are arranged on opposite sides of the intake valve driving means 17₄ beyond the camshaft 16 and therefore it is possible to secure a relatively large space between the exhaust valve rocker arms 29₄ and 30⁴. In addition, the exhaust valves VE1 and VE2 can be arranged at a relatively large distance from each other so that the plug tube 65 can be arranged in the cylinder head 2 between the exhaust valves VE1 and VE2 as well as between the exhaust valve side rocker arms 29₄ and 30₄.

In such a fourth embodiment, in a high speed operating state of the engine, the first and second driving rocker arms 24₄ and 25₄ and the free rocker arm 26₄ are connected to each other so that the intake valves VI1 and VI2 can be opened and closed at a timing and a lift amount corresponding to the shape of the high speed cam 21. In a low speed operating state of the engine, the connection of the first driving rocker arm 24₄ and the free rocker arm 26₄ can be released as well as the connection of the free rocker arm 26₄ and the second driving rocker arm 25₄ so that the first intake valve VI1 can be opened and closed by the first driving rocker arm 24₄ at a timing and a lift amount corresponding to the shape of the low speed cam 22. which is in rolling contact with the low speed cam 22, while the second drive rocker arm 25₄ which is in sliding contact with the raised portion 8 can be brought into a substantially inoperative state to second inlet valve VI2 is essentially rendered inoperative.

The first drive rocker arm 24₄, which operates in a low speed range, is in rolling contact with the low speed cam 22 via the roller 89, which can contribute to a reduction in friction loss in the valve actuation system in the low speed range and, consequently, to a reduction in friction loss in the entire engine. In addition, since the exhaust valve side rocker arms 29₄ and 30₄ are also in rolling contact with the exhaust valve cam 23, 23 via the rollers 86 and 87, it is possible to provide a further reduction in friction loss in the low speed range.

Further, the second drive rocker arm 25₄ is in sliding contact with the raised portion 80 via the slider 91 and therefore the width of the slider 91 can be smaller than that of the roller 89. This ensures that the intake valve drive means 17₄ can be made more compact along the axis of the camshaft 16 as compared with those in the above first and second embodiments.

Moreover, notwithstanding the provision of the connection switching mechanism 50 in the intake valve driving means 174, the entire arrangement can be made compact as in the above embodiments.

In the foregoing embodiments, the connection switching mechanism has been described as being provided in the rocker arms constituting the intake valve driving means for switching between the connection and the disconnection of all the rocker arms, but it is to be understood that the connection switching mechanism may be designed to switch between the connection and the disconnection of only a pair of adjacent rocker arms.

Thus, in at least preferred embodiments, there is provided a SOHC internal combustion engine comprising a pair of intake valves and a pair of exhaust valves, wherein the intake valve driving means can be made compact, the opening and closing mode of the intake valves can be changed in accordance with the operating state of the engine; and wherein a space for arranging the cylindrical plug receiving portion is ensured, while a compact overall valve operating system is provided; and wherein friction reduction is provided in the low speed range in which the component of the friction loss in the entire engine in the valve operating system forms a larger proportion, and thus friction loss reduction in the entire engine is provided, and wherein a compact construction of the intake valve driving means is provided.

Claims (3)

1. Multi-cylinder internal combustion engine with a single overhead camshaft, comprising: a plurality of cylinders (3); a single camshaft (16) rotatably mounted in a cylinder head (2) above combustion chambers (5) for the cylinders, wherein cams (21, 22, 23) are provided on the single camshaft (16); a pair of intake valves (VI1, VI2) for each cylinder (3) mounted in the cylinder head (2) on one side of the camshaft (16); a plurality of intake valve side drive rocker arms (24₁, 25₁, 26₁; 24₂, 25₂, 26₂; 24₃, 25₃; 24₄, 25₄, 26₄) for operatively connecting the camshaft (16) to the pair of intake valves (VI1, VI2); a pair of exhaust valves (VE1, VE2) for each cylinder (3) mounted on the cylinder head (2) on the other side of the camshaft (16); a pair of exhaust valve side drive rocker arms (29₁, 30₁; 29₂, 30₂; 29₃, 30₃; 29₄, 30₄) for operatively connecting the camshaft (16) to the pair of exhaust valves (VE1, VE2); an arrangement for rotatably holding the camshaft (16) on the cylinder head (2); a spark plug mounting hole in a central portion of a ceiling of each combustion chamber (5); and a candle tube (65) which extends to the Spark plug mounting hole and is provided in an inclined manner with its upper portion spaced from the camshaft (16), the plug tube (65) being arranged substantially between the camshaft (16) and the axes of the pair of exhaust valves (VE1, VE2); wherein the plurality of intake valve side drive rocker arms (24₁, 25₁, 26₁; 24₂, 25₂, 26₂; 24₃, 25₃; 24₄, 25₄, 26₄) are positioned between the pair of exhaust valve side drive rocker arms (29₁, 30₁; 29₂, 30₂; 29₃, 30₃; 29₄, 30₄); characterized, that the support arrangement comprises adjacent two holders (20; 71) which are coupled to the cylinder head (2), wherein the adjacent two holders (20; 71) are each located between two adjacent cylinders (3) and form adjacent supports for the camshaft (16) and wherein the plurality of intake valve side drive rocker arms (24₁, 25₁, 26₁; 24₂, 25₂, 26₂; 24₃, 25₃; 24₄, 25₄, 26₄) and the pair of exhaust valve side drive rocker arms (29₁, 30₁; 29₂, 30₂; 29₃, 30₃; 29₄, 30₄) all arranged between the adjacent two holders (20; 71) at a location substantially above the associated cylinder (3); wherein the cams (21, 22, 23) for operating the intake and exhaust valve side drive rocker arms (24₁, 25₁, 26₁; 24₂, 25₂, 26₂; 24₃, 25₃; 24₄, 25₃, 26₄ and 29₁, 30₁; 29₂, 30₂; 29₃, 30₃; 29₄, 30₄) for each cylinder are all arranged between the adjacent two holders (20; 71), the cams (23) for the exhaust valve side drive rocker arms being located at opposite outermost positions; and wherein a mechanism (50; 50') for switching between a connection and a disconnection between adjacent ones of intake valve side drive rocker arms (24₁, 25₁, 26₁; 24₂, 25₂, 26₂; 24₃, 25₃; 24₄, 25₄, 26₄). 2. Multi-cylinder internal combustion engine with a single overhead camshaft according to claim 1, characterized in that a rocker arm shaft (28) for supporting the exhaust valve side drive rocker arms (29₁, 30₁; 29₂, 30₂; 29₃, 30₃; 29₄, 30₄) is arranged in the cylinder head (2) in such a way that it is arranged substantially parallel to the camshaft (16) at a location closer to the pair of exhaust valves (VE1, VE2), the spark plug tube (65) being located between the rocker arm shaft (28) and the axes of the exhaust valves (VE1, VE2). 3. A multi-cylinder single overhead camshaft internal combustion engine according to claim 1 or 2, characterized in that the plurality of intake valve side drive rocker arms comprises a free rocker arm (26₁; 26₂; 26₄) operable during a particular engine operation, and a lost motion mechanism (38; 38') is provided in operative association with the free rocker arm on a member (37) supported above the adjacent two brackets (20; 71).